1. Field of the Invention
The invention relates to a reflective X-ray microscope for examining an object in an object plane, with the object being illuminated with radiation of a wavelength ≦100 nm, especially <30 nm, and imaged in an enlarged way in an image plane. Such a reflective X-ray microscope comprises a first subsystem which is arranged in the beam path from the object plane to the image plane and which comprises at least one first optically imaging element, preferably a first mirror.
2. Description of the Related Art
X-ray microscopes are known from the following applications:                U.S. Pat. No. 5,222,113        U.S. Pat. No. 5,311,565        U.S. Pat. No. 5,177,774        U.S. Pat. No. 5,144,497        U.S. Pat. No. 5,291,339        U.S. Pat. No. 5,131,023 EP-A-0 459 833        
A Schwarzschild optical system with downstream diffraction grating is known from                U.S. Pat. No. 5,022,064,and an inspection system with reflective X-ray microscope is known from        JP-A-2001116900.        
U.S. Pat. No. 5,222,113, U.S. Pat. No. 5,311,565, U.S. Pat. No. 5,177,774, and EP-A-0 459 833 show X-ray microscopes in which zone plates are provided in the projection lens system for imaging. The Fresnel zone plate is a wave-optical imaging component in which the light is diffracted in a system of concentrically arranged circular rings. The disadvantage of using Fresnel zone plates in imaging systems with several optical elements in the X-ray-wavelength region is that Fresnel zone plates are transmittive components which lead to high losses of light due to the low transmission in the X-ray wavelength range.
X-ray microscopes comprising Schwarzschild optical systems as imaging systems are known from the U.S. Pat. No. 5,144,497, U.S. Pat. No. 5,291,339 and U.S. Pat. No. 5,131,023.
In all X-ray microscopes described in the U.S. Pat. No. 5,144,497, U.S. Pat. No. 5,291,339 and U.S. Pat. No. 5,131,023, the beam path at the object to be examined is designed in a telecentric way, which renders the imaging of objects in reflection more difficult.
A further disadvantage of such systems for the use in examining objects, and especially such used in the area of X-ray lithography, is their large overall size for achieving adequate lateral magnification. This makes their use in inspection systems for examining masks in EUV projection illumination systems more difficult.
A Schwarzschild optical system is known from U.S. Pat. No. 5,022,064 in which a diffraction grating is arranged according to the Schwarzschild optical system in order to diffract X-rays of different wavelengths into different orders and to thus split up the light in a spectral way. This system is also telecentric at the object.
A reflective X-ray microscope for examining an object for microlithography in an object plane with radiation of a wavelength <100 nm, especially 30 nm, is known from JP-A-2001116900. The X-ray microscope as disclosed in this application is a Schwarzschild optical system with a concave first mirror and a convex second mirror. In contrast to the systems as described above, the beam path for examining the object is not telecentric on the object, so that an examination in reflection of EUV reflection masks for example is enabled.
The disadvantage of a system as disclosed by JP-A-2001116900 is that it has a very large overall size when a large lateral magnification is required.